Columns used in liquid chromatography typically comprise a tubular body enclosing a porous chromatography medium through which a carrier liquid flows, with separation taking place by material collection between the carrier liquid and solid phase of the porous medium. Typically, the medium is enclosed in the column as a packed bed formed by consolidating a suspension of discrete particles, known as slurry that is pumped, poured, or sucked into the column. Consolidation of the slurry into a packed bed is achieved by compressing the slurry so that it is packed into a volume, which is less than the volume that it would have occupied if it had been allowed to settle under the influence of gravity to form a sedimented bed. The efficiency of subsequent chromatographic separation relies strongly on 1) the liquid distribution and collection system at the fluid inlet and outlet of the packed bed, 2) on the special orientation (also know as the packing geometry) of the media particles in the packed bed, and 3) on the compression of the packed bed. If the compression of the packed bed is too low then chromatographic separations performed on that bed suffer from “tailing” and, generally, such insufficiently compressed beds are unstable. If the compression of the packed bed is too high then chromatographic separations performed by the bed suffer from “leading” and such over-compressed beds can affect throughput and binding capacity, and, in general, give much higher operating pressures. If the compression is optimum, then the separation peaks formed during use exhibit much less leading or tailing and are substantially symmetrical. The optimum degree of compression required for a column is determined experimentally for each column size (width or diameter), bed height, and media type.
Prior to any separation process, the bed has to be prepared by starting from the slurry of particles that has to be introduced into the column. The process of bed formation is called ‘the packing procedure’ and a correctly packed bed is a critical factor influencing the performance of a column containing a packed bed. One of the primary goals of the packing procedure is to provide a bed, which is compressed by the optimum amount of compression, i.e. the optimum compression factor. The height of the bed when it is optimally compressed is called the target compressed bed height.
Large-scale columns, such as CHROMAFLOW™ (which is a registered trademark of GE Healthcare are columns manufactured by GE Healthcare in Piscataway, N.J.), CHROMAFLOW™-like columns and other columns presently utilized in the industry, are preferably packed by delivering it into the column, through a central slurry nozzle, media valve, or another port, a predetermined volume of slurry having a specified concentration of media particles. Once the predetermined volume of slurry has been delivered into the column, the chromatography medium in the column may be either 1) fully packed or 2) not packed and in need to be further consolidated and compressed by moving a movable adapter down the longitudinal axis of the column towards the bottom of the column, normally at a constant speed. The excess liquid during this procedure is expelled at the column outlet, while the media particles are retained by means of a filter material, a so-called ‘bed support’, with pores too small to allow the media particles to pass though. The packing process is complete once the packed bed has been compressed by the optimum amount or degree of compression. The packing process is considered successful if the compressed bed allows for a good and robust chromatographic performance. However, packing such an optimally compressed bed of chromatography media in a chromatography column by manual means is not easy to accomplish in practice due to the fact that the quality of the final packed bed depends to a great extent on the skill of the operator. During filling and subsequent packing of the column, the operator manually selects and adjusts all packing parameters such as valve positions, pump speed, flow rates, adapter's speed of movement, etc. More importantly, in all cases, the operator has to arbitrarily decide when the column packing should end by visually determining that either 1) sufficient slurry has been delivered into the column or 2) that the adapter has sufficiently compressed the bed. Mistakes in the selection of any of the packing parameters, and/or mistakes in the decision on when to end the packing, normally lead to a poorly performing column. Further, in columns equipped with a transparent tube it is particularly difficult, and in columns equipped with a non-transparent tube such as stainless steel it is impossible, to judge by eye when compression of the bed actually starts and a significant error at this point makes it impossible to obtain an optimally compressed bed. In sum, column packing has hitherto been regarded as an art rather than a science.
Therefore, there is a need for a system and method for the accurate and reproducible packing of chromatography media into chromatography columns.